1. Field of the Embodiment
The embodiment relates generally to a stamping die and more particularly to a method for designing a stamping die and a stamping die for use in producing sheet metal parts.
2. Description of Related Art
Stamping dies are used for producing sheet metal parts. A toggle draw die is one type of draw die assembly used to form sheet metal, particularly when the metal part has a complex geometry and requires deep drawing. Toggle draw dies account for approximately 40% of all stamping dies. A toggle draw die assembly usually includes 3 main components, often referred to as a draw punch, a die cavity and a binder ring. It may include other components such as die shoes, guideposts, adaptor plates and wear plates. Each component has a particular function while at the same time interacting with the other components. For example, one function of the binder ring is to control the metal flow by applying pressure to the sheet metal lying between the binder and the lower die cavity during the forming process. In addition, the binder ring also serves as a guide for the punch.
During a stamping cycle a draw die assembly often undergoes complex loading conditions, particularly in cases where an unbalanced forming force exists. An unbalanced forming force typically occurs and is often significant when the part is non-symmetrical, which holds true for most parts. An unbalanced forming force occurring during the forming operation can cause the punch to deviate from its vertical position and interact with the binder ring in the lateral direction thus creating a lateral force on the binder ring. Similarly, the binder ring and the lower cavity may also experience contacting interaction in the form of a lateral force.
Interacting lateral forces occurring between the various components caused by unstable and undesirable punch motion, can create failure modes for the die structure including cracking or breaking of the die and excessive die deformation. When die cracking occurs, dies have to be removed from production for repair, if repairable. The die may be reconstructed or a new die must be designed and built if the old die or component thereof is not repairable, a process which normally takes months to complete. The new or repaired die must be tried out again before resuming production. Manufacturing losses resulting from such failures, including lost production and market share can be costly. For example, in addition to a manufacturer incurring assembly plant down time and corresponding lost production costs, the manufacturer will also incur additional costs associated with any redesign, repair and rebuild of the die assembly.
Lateral forces occurring between the various components can also lead to excessive die deformation. Excessive die deformation can cause issues with stamping quality as die deformation often leads to poor control of the binder pressure and consequently poor control of the metal flow.
Since die design is primarily based on generic standards and prior experience of the designer, the performance expectations of many die designs are unknown. Some are under designed while others are over designed. This can lead to prolonged die tryout and setup which can delay production along with increasing costs due to die failure. Accordingly, there are many challenges related to die engineering and design regarding die cost reduction and performance improvement.